The present invention generally relates to the art of concrete construction, and more particularly to a device for facilitating the placement of slip dowel rods within a concrete slab.
In the art of concrete construction, it is commonplace to form "cold joints" between two or more poured concrete slabs. Such cold joints frequently become uneven or buckled due to normal thermal expansion and contraction of the concrete and/or compaction of the underlying soil caused by inadequate substrate preparation prior to pouring of the concrete. As a means of preventing buckling or angular displacement of such cold joints, it is common practice to insert smooth steel dowel rods generally known as "slip dowels" within the edge portions of adjoining concrete slabs in such a manner that the concrete slabs may slide freely along one or more of the slip dowels, thereby permitting linear expansion and contraction of the slabs while at the same time maintaining the slabs in a common plane and thus preventing undesirable buckling or unevenness of the cold joint and in adjacent slabs.
In order to function effectively, slip dowels must be accurately positioned parallel within the adjoining concrete slabs. The non-parallel positioning of the dowels will prevent the desired slippage of the dowels and will defeat the purpose of the "slip dowel" application. Additionally, the individual dowels must be placed within one or both of the slabs in such a manner as to permit continual slippage or movement of the dowels within the cured concrete slab(s).
It is commonplace to form large concrete slabs using monolithic or continuous concrete pour methods. Such slabs are formed by continuously pouring large quantities of concrete without the use of forms or cold joints in order to reduce costs. Therefore, fracturing of the slab is prevented by including tooled joints or sawcuts in the slab where cold joints would otherwise be needed. Additionally, concrete reinforcement material such as wire mesh or segments of rebar are initially placed into the area in which the continuous pour is to be made, and in particular those areas where it is contemplated that sawcuts will be included in the resultant slab for purposes of preventing fracturing thereof. The wire mesh or other reinforcement material is preferably elevated above ground level by the placement thereof upon support blocks or "chairs".
In addition to having concrete reinforcement material disposed within those portions of the slab in which a sawcut is to be made, it is also desirable to incorporate slip dowels into such portions to allow the separate sections of the slab which are defined by the sawcuts to move relative to each other while preventing any buckling or angular displacement thereof. One prior art method of incorporating slip dowels into those areas of a continuous pour where sawcuts are contemplated involves manually "stabbing" the slip dowels into predetermined locations of the uncured concrete pour. This method, however, is deficient in that there is no way to insure that the slip dowels will be manually positioned within the uncured concrete in parallel relation to each other, or will be maintained in parallel alignment to the top surface of the concrete pour during curing. As previously explained, if the dowel rods are not in parallel alignment, the separate sections of slab as defined by the sawcuts will be prevented from moving relative to each other.
Another prior art method of incorporating slip dowels into a monolithic pour involves manually tieing the slip dowels to the reinforcement material in parallel relation to each other prior to the concrete pour being made. Manual tieing, however, is extremely time consuming and presents significant difficulties in securing the slip dowels to the reinforcement material in true parallel relation to each other. Additionally, the tied slip dowels are susceptible to displacement or shifting when impacted by the concrete during the pour thus moving the same out of parallel alignment with each other.
The present invention addresses and overcomes the above-described deficiencies of prior art slip dowel placement in continuous concrete pours by providing a device that places slip dowels accurately during the pouring of such concrete slabs. In this respect, the present invention places slip dowels into a concrete slab through the use of slip tubes that are easily attached to a prefabricated support structure. Therefore, the present invention provides an accurate and easy system for slip dowel placement in a monolithic pour.